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zlib Home Site
A Massively Spiffy Yet Delicately Unobtrusive Compression Library
(Also Free, Not to Mention Unencumbered by Patents)
(Not Related to the Linux zlibc Compressing File-I/O Library)
Welcome to the zlib home page, web pages originally created by
Greg Roelofs
and maintained by Mark Adler.
If this page seems suspiciously similar to the
PNG Home Page, rest assured
that the similarity is completely coincidental. No, really.
zlib was written by
Jean-loup Gailly (compression) and
Mark Adler
(decompression).
Current release:
zlib 1.2.11
January 15, 2017
Version 1.2.11 has these key improvements over 1.2.10:
Fix deflate stored bug when pulling last block from window
Permit immediate deflateParams changes before any deflate input
Due to the bug fixes, any installations of 1.2.9 or 1.2.10 should be immediately replaced with 1.2.11.
Version 1.2.10 has these key improvements over 1.2.9:
Fix bug in deflate_stored() for zero-length input
Fix bug in gzwrite.c that produced corrupt gzip files
Version 1.2.9 has these key improvements over 1.2.8:
Improve compress() and uncompress() to support large lengths
Allow building zlib outside of the source directory
Fix bug when level 0 used with Z_HUFFMAN or Z_RLE
Fix bugs in creating a very large gzip header
Add uncompress2() function, which returns the input size used
Dramatically speed up deflation for level 0 (storing)
Add gzfread() and gzfwrite(),
duplicating the interfaces of fread() and fwrite()
Add crc32_z() and adler32_z() functions with size_t lengths
Many portability improvements
You can also look at the complete Change Log.
Canonical URL:
http://zlib.net/ (US)
zlib is designed to be a free,
general-purpose, legally unencumbered -- that is, not covered by any patents
-- lossless data-compression library for use on virtually any computer hardware
and operating system. The zlib data format is itself portable across
platforms. Unlike the LZW compression method used in Unix compress(1)
and in the GIF image format, the compression method currently used in zlib
essentially never expands the data. (LZW can double or triple the file size in
extreme cases.) zlib's memory footprint is also independent of the input data
and can be reduced, if necessary, at some cost in compression. A more precise,
technical discussion of both points is available on
another page.
zlib was written by
Jean-loup Gailly (compression) and
Mark Adler
(decompression). Jean-loup is also the primary author of
gzip(1), the author of the comp.compression FAQ list and
the former maintainer of
Info-ZIP's Zip;
Mark is also the author of gzip's and
UnZip's main
decompression routines and was the original author of Zip. Not surprisingly,
the compression algorithm used in zlib is essentially the same as that in
gzip and Zip, namely, the `deflate' method that originated in
PKWARE's PKZIP 2.x.
Mark and Jean-loup can be reached by e-mail at
.
Please read the FAQ and
the manual before asking
us for help. We are getting too many questions which already have an
answer in the zlib documentation.
The deflate and zlib specifications both achieved official Internet RFC status in May 1996,
and zlib itself was adopted in version 1.1 of the Java Development Kit (JDK), both as a
raw class and as a component of the JAR archive
format.
The lovely zlib-vise image above was provided courtesy of Bruce Gardner, art
director of Dr. Dobb's Journal. It
appears in Mark Nelson's article in the January 1997 issue (see below).
The current release is publicly available here:
zlib source code, version 1.2.11, tar.gz format (593K,
SHA-256 hash c3e5e9fdd5004dcb542feda5ee4f0ff0744628baf8ed2dd5d66f8ca1197cb1a1):
US (zlib.net) (GPG signature)
Pick a mirror (prdownloads.sourceforge.net)
zlib source code, version 1.2.11, tar.xz format (457K,
SHA-256 hash 4ff941449631ace0d4d203e3483be9dbc9da454084111f97ea0a2114e19bf066):
US (zlib.net) (GPG signature)
Pick a mirror (prdownloads.sourceforge.net)
zlib source code, version 1.2.11, zipfile format (730K,
SHA-256 hash d7510a8ee1918b7d0cad197a089c0a2cd4d6df05fee22389f67f115e738b178d):
US (zlib.net) (GPG signature)
Pick a mirror (prdownloads.sourceforge.net)
Note that zlib is an integral part of
libpng and
has been tested extensively as part of many
PNG-supporting
applications.
zlib Information
zlib Frequently Asked Questions
Zlib-announce mailing list
New versions of zlib are announced on this list.
DD
Zlib-devel mailing list
Please do not send questions or comments about zlib to
this mailing list. Send those directly to the authors at
after checking the FAQ and
the manual, of course. The zlib-devel list is for the development of
zlib mdash;members are contributors to and testers of new versions of zlib.
DD
zlib Manual
zlib Usage Example
zlib Technical Details
zlib-related specifications:
RFC 1950 ZLIB Compressed Data Format Specification version 3.3
RFC 1951 DEFLATE Compressed Data Format Specification version 1.3
RFC 1952 GZIP file format specification version 4.3
Deflate stream disassembler.
infgen.c produces a readable description of a gzip, zlib, or
raw deflate stream.
zlib's Deflate Algorithm
zlib's deflate flush modes
zlib License
All released versions of zlib
zlib on github
CRC (Cyclic Redundancy Check) Bonus Information
Ross Williams' classic "A Painless Guide to CRC Error Detection Algorithms"
Code to generate any CRC, with a list of CRC
descriptions. crcany.c can take a description of a CRC and
compute that CRC efficiently. It includes bit-wise, table-driven
byte-wise, and table-driven word-wise CRC algorithms.
Code to modify a message so that it generates the
desired CRC. spoof.c takes an abbreviated description of
the CRC, the exclusive-or of the current CRC of the message and the
desired CRC, the length of the message, and a list of bit locations in
a message, and tells you which of those bits should be inverted in the
message to get the desired CRC. Note that it does not need the message
itself, due to the linearity property of CRCs.
ZIP File Processing Bonus Software
Code to read a zip file as a stream and extract
its contents. sunzip.c will read a zip file from stdin
and extract the files therein that use compression methods 0, 8, 9, or
12 (stored, deflate, deflate64, or bzip2). It accepts Zip64 input.
Code to merge multiple zip files into a single
zip file. zipknit.c accepts Zip64 input files, and will
create Zip64 output if the combined size of the merged zip file
warrants it. All compression formats are permitted, since no
decompression or recompression is performed. Encrypted entries are
permitted, and pass through unscathed.
Related External Links
zlib for Linux, both shared and
static plus headers (RPM format, many
architectures)
zlib for Solaris (alternate)
zlib for macOS (Mac OS X): zlib is already included as part of macOS
zlib for Palm Pilot
zlib for Newton OS
zlib for Windows CE
zlib for Windows
9x/NT/2000/XP/2003 (DLL version, plus related utilities)
zlib for Windows 9x/NT (DLL and static version)
DotNetZip zip file manipulation for .NET, and more (including replacements for the
buggy Microsoft GZipStream and DeflateStream classes)
zlib for .NET in C#
zlib DLL wrapper for .NET in C#
Zip for .NET
Mark Nelson's
ZlibTool article (January 1997)
zlib C++ wrapper for the gz* functions.
C++ zlib and gzip filters in an iostream framework.
zlib
32-bit OCX
(C++ source and binaries for use with Visual Basic 4.x or
Delphi 2.0)
(unsupported VB5 binary also available)
DD
zlib Delphi 5 interface
(includes compiled object files and corresponding C++ Builder 5
project files)
DD
zlib Perl interface (source code; look for Compress-Zlib*.tar.gz)
zlib Python
interface (online manual; part of the standard library as of
Python 1.5)
zlib Tcl
interface mkZiplib
zlib Haskell
interface
zlib Java interface (see also JAR format)
zlib reimplementation in pure
Java
(not tested by us, but looks like a good alternative to
java.util.zip)
DD
Mark Nelson's
JavaZip article (with source code) (December 1997)
Random access for gzip archives, for Java
Gilles Vollant's zlib-based
mini-zip and
mini-unzip
(see also Info-ZIP's UnZip,
which optionally can be compiled with zlib)
DD
Scott Ludwig's zlib-based
CExe executable compressor for Win32
zlib technical issues, including spec errors
zlib information in Japanese
zlib information in Russian
Real World Scanning and Halftones
(second edition includes a section on zlib)
Markus Oberhumer's
LZO `real-time' data compression library
(not tested by us, but looks like a good alternative if you need
more speed and less compression)
DD
lz4, a very fast compression algorithm
(not tested by us, but looks like an even better alternative if you need
more speed and less compression)
DD
Zstandard, a better compression algorithm
(not tested by us, but appears to be a better alternative to zlib
in both dimensions of compression and speed, as well as
decompression speed)
DD
libbzip2
(not tested by us, but looks like a good alternative if you need
more compression and less speed)
DD
PPP Deflate Protocol
(RFC 1979)
Info-ZIP Home Page
Portable Network Graphics (PNG)
Home Page
gzip Home Page
pigz (parallel gzip) Home Page
DataCompression.info
comp.compression Frequently Asked Questions list
Send comments or questions about zlib to the authors at
after checking FAQ and
manual.
Please report broken links to
(PGP key).
This page last updated December 15th, 2017.
Web page copyright #169; 1996-2017
Greg Roelofs,
Jean-loup Gailly and
Mark Adler.
zlib software copyright #169; 1995-2017
Jean-loup Gailly and
Mark Adler.
zlib.org domain name donated by Andrew Green.